As an apparatus for non-invasively measuring internal information of a living body such as a head and a breast, an apparatus which makes use of light absorbing characteristics of a living body to obtain the internal information, that is, an apparatus which uses so-called diffuse optical tomography (DOT; Diffuse Optical Tomography), has been proposed. With such a measuring device, a region of a living body to be measured is irradiated with light from a predetermined irradiation position, and light which is propagated while being scattered in an inside of the region is detected at a predetermined detection position. Then, internal information on the region, that is, information on a light absorbing body such as a tumor, etc., present in the inside of the region can be obtained from measurement results of intensity, time waveform, etc. For example, Non-Patent Document 1 has described a method for conducting three-dimensional optical imaging of a living body by the use of a multi-channel time-resolved spectroscopic measurement apparatus.